It was recently demonstrated that when papilloma-bearing mice were treated with certain tumor initiators and promoters malignant progression was markedly enhanced, whereas TPA was found to be ineffective in malignant progression. This proposed investigation seeks to determine the critical changes and factors that occur in the conversion of papillomas to squamous cells carcinomas. We propose to pursue the following specific aims: 1) Since benzoyl peroxide and ENU were found to be the most active agents in enhancing malignant progression, we will determine what treatment conditions, such as dose, number of applications and route of administration, are the most effective. Once optimum treatment conditions are established,we will determine the effectiveness of benzoyl peroxide and ENU on enhancing the malignant progression of papillomas with different characteristics and/or potential to progress. 2) We will establish an in vitro model for malignant progression using a mouse epidermal cell line derived from MNNG-TPA treatment in vivo and a mouse papilloma cell line derived from DMBA-TPA induced papilloma. At various times following treatment of the cells with either benzoyl peroxide or ENU, the cells will be examined for growth characteristics in subcutaneous chambers on host mice and in nude mice. 3) We will determine the effectiveness of other carcinogens, initiators, and promoters as enhancers of malignant progression. 4) We will determine the effectiveness of certain inhibitors of carcinogenesis on malignant progression induced by various agents in both the in vivo and in vitro models. 5) We will determine if enhancers of malignant progression alter the expression of various early markers of malignant progression such as loss of high molecular weight keratins, presence of GGT and chromosomal alterations. 6) Since both papillomas and carcinomas are comprised of a heterogeneous population of cells, we will develop the necessary methodology to isolate and characterize the critical cell population involved in malignant progression. Percoll gradient separation, elutriation, and cell sorter analysis will be used to isolate subpopulations of cells for characterization with respect to the above markers as well as for altered expression of several oncogenes. These proposed in vivo and in vitro studies should provide a better understanding of agents found to be effective enhancers and inhibitors and should contribute to a better knowledge of the cellular and molecular mechanism involved in malignant progression.